Implement Custom Elements 'extends' option.

Implement Custom Elements 'extends' option.

This enables creating type extensions of elements without a
differentiated prototype, like <section> (whose interface is
HTMLElement) and elements without a distinct prototype, like <ins> and
<del> (whose interface is HTMLModElement.)

This relaxes a lot of prototype chain checks, in line with recent
changes in the spec Working Draft.

BUG=234509
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=157559

[dominicc (has gone to gerrit), 2013-09-10 02:41:39]

PTAL

[Hajime Morrita, 2013-09-10 03:48:27]

lgtm.

[dominicc (has gone to gerrit), 2013-09-10 05:17:12]

On 2013/09/10 03:48:27, morrita1 wrote:
> lgtm.

Thanks!

<https://codereview.chromium.org/23702032/> has to go first so we don't break
<webview>.

[dominicc (has gone to gerrit), 2013-09-10 05:21:52]

dglazkov: bindings/v8 left needing OWNERs, comments on everything welcome.

[dglazkov, 2013-09-10 15:29:58]

lgtm.

[commit-bot: I haz the power, 2013-09-10 22:57:40]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dominicc@chromium.org/23717043/1

[commit-bot: I haz the power, 2013-09-11 01:01:12]

Change committed as 157559